1. Field of the Invention
The present invention is directed to new (cyclopropyl)vinyl alkyl ether derivatives and to a process for the preparation of these derivatives.
2. Description of the Prior Art
The cyclopropanecarboxylate esters are insecticidally-active compounds known as "pyrethroids" and as they combine exceptionally good insecticidal properties with a very low mammalian toxicity, they are of great interest to the agrochemical industry. Therefore, considerable effort has been expended in finding economic routes to them and to their principal intermediates.
The general formula of one class of these pyrethroids may be represented as follows: ##STR3## wherein each asterisk denotes a chiral carbon atom; each X is a halogen atom and R is a member of a group of radicals known to impart insecticidal activity to the molecule, e.g. 3-phenoxybenzyl or alpha-cyano-3-phenoxybenzyl. It is known that for maximum insecticidal activity the stereoisomeric form of the acid part of the ester of the above-mentioned formula should be 1R,cis, i.e. the absolute configuration at carbon atom 1 is R and the two hydrogen atoms on carbon atoms 1 and 3 are in a cis relationship. This nomenclature is known as the Elliott nomenclature and is defined in M. Elliott c.s., Nature, 1974, 248, 710.
It follows, therefore, that if 1R,cis esters of the abovementioned formula are to be prepared, either a stereo-specific chemical route is required or the desired stereoisomer must be obtained from a racemic mixture by physical separation techniques. The latter techniques are expensive and laborious and not readily employed on an industrial scale. The Applicant has found two stereo-specific routes which use as starting material the naturally-occurring substance (+)-3-carene whose formula is as follows: ##STR4## This compound is an inexpensive, readily available natural terpene. The present application discloses two routes to the (1R,cis)-acid portion of the pyrethroid ester mentioned hereinbefore, starting from (+)-3-carene and proceeding via novel cyclopropane compounds according to the invention.